The 3rd Generation Partnership Project (3GPP) has a project called Long Term Evolution (LTE) to improve the Universal Mobile Telecommunication System (UMTS) standard, which among other things improves data services over wireless communication networks. The LTE standard includes a number of features to provide higher data rates, increased system capacity, and improved spectral efficiency. These features include the use of orthogonal frequency division multiplexing (OFDM) and a multiple-input, multiple-output (MIMO) scheme in the downlink. In order to maintain backward compatibility with existing spectrum allocations for, e. g., GSM and WCDMA, the LTE systems will be able to operate on bandwidths ranging from 1.4 MHz to 20 MHz. Like WCDMA systems, the same frequencies will be used in adjacent cells. Therefore, it is important that the mobile terminals be capable of suppressing inter-cell interference.
In the case of a mobile terminal with two receive antennas, diversity-combining can be employed to improve the signal-to-noise ratio and reduce interference. Various techniques for diversity-combining are known, including equal gain combining (EGC), maximum ratio combining (MRC), and interference rejection combining (IRC). EGC is a simple combining scheme that does not require a noise estimate. MRC requires an estimate of the channel power and noise power for each antenna, while IRC requires an estimate of the noise color. Assuming that good channel estimates and noise estimates can be obtained, IRC is usually better than MRC and EGC.
The channel estimates and noise estimates are usually obtained from pilot symbols. In general, increasing the number of pilot symbols transmitted improves channel and noise estimation at the expense of greater signaling overhead. Decreasing the number of pilot symbols transmitted can negatively impact the quality of the channel and noise estimates. When there are an insufficient number of pilot symbols to generate accurate channel and noise estimates, IRC may not provide any improvement over MRC, and may even be worse.
Accordingly, there is a need for new methods for generating accurate channel and noise estimates for interference cancellation and suppression.